The proposed research will extend previous observations indicating that immune processes are subject to behavioral conditioning. Using an illness-induced taste aversion paradigm, rats and/or mice will be conditioned by pairing a distinctively flavored drinking solution (the conditioned stimulus) with an immunosuppressive agent (e.g., cyclophosphamide, methotrexate, vinblastine), the unconditioned stimulus. After conditioning, all animals will be injected with antigen (e.g., SRBC, TNP-LPS). Antibody titers will be measured after antigen administration in conditioned animals that are again exposed to the conditioned stimulus or that receive no further experimental treatment, and in non-conditioned and placebo-treated groups. In addition to assessing immunosuppression associated with thymus dependent and thymus independent humoral responses, the effects of conditioning on cell-mediated responses (host-vs-graft reaction, delayed hypersensitivity) will be studied. The biological significance of conditioned immunosuppression will also be assessed by measuring the immune responses and ultimate survival of mice to an experimentally-induced parasitic disease, the rodent malaria, Plasmodium berghei, and a spontaneously developing autoimmune disease in NZBxNZW mice which is an experimental model of systemic lupus erythematosus in humans, both of which are sensitive to the effects of immunosuppressive chemotherapy.